Platelet activating factor (PAF) is a recently-identified phosphoglyceride that induces platelet aggregation, prostaglandin formation and platelet granule secretion. The first priority of this application is to determine whether the sudden formation or release of PAF in the platelet membrane can account for that component of platelet activation not attributable to ADP release or prostaglandin formation. Subsequent aims include determinations of changes in the different phosphoglycerides of platelets and other cells that are associated with PAF formation, measurements of the enzymes involved in PAF formation and degradation, and measurements of the binding and release of 3H-PAF by human and rabbit platelets. Suspensions of human platelets or rabbit platelets, leukocytes or macrophages will be treated for short time intervals in vitro with different agents and then the phospholipid-like compounds will be extracted using organic solvents. PAF will be purified by high performance liquid chromatography and measured using a bioassy based on its ability to induce rabbit platelet aggregation in vitro. Cellular phospholipids with be labelled with 32P and changes in radioactive PAF as well as other phospholipids will be measured.